U.S. patent number 3,832,056 [Application Number 05/234,018] was granted by the patent office on 1974-08-27 for distance measuring device using electro-optical techniques.
This patent grant is currently assigned to AGA Corporation. Invention is credited to Thomas D. Broadbent, Robin H. Hines, William L. Hollinshead, John I. Shipp.
United States Patent |
3,832,056 |
Shipp , et al. |
August 27, 1974 |
DISTANCE MEASURING DEVICE USING ELECTRO-OPTICAL TECHNIQUES
Abstract
An electro-optical surveying instrument for measuring distance
utilizing a frequency modulated laser beam is provided with special
positioning of lenses so that there is an internal calibration for
the lenses utilized so that an exact measurement can be made of a
distance from the plumb point of the instrument to the
retroreflector at the point from which the distance is being
measured. A digital signal level indicator is provided to give the
operator of the instrument an exact indication of the strength of
the return beam so that he knows exactly whether a reading can be
made under a given condition. Electronic logic is provided within
the instrument to cancel all second harmonic distortions. The
surveying instrument itself is provided with a photo optical switch
which allows the instrument to be turned on or off without the need
for touching the instrument so as not to in any way affect the
exact position of the instrument when a reading is being made.
Further, a minimum number of frequencies are utilized to modulate
the laser beam while receiving the same range as with instruments
utilizing greater numbers of frequencies to modulate the laser.
Inventors: |
Shipp; John I. (Tullahoma,
TN), Hines; Robin H. (Tullahoma, TN), Hollinshead;
William L. (Tullahoma, TN), Broadbent; Thomas D.
(Tullahoma, TN) |
Assignee: |
AGA Corporation (Secaucus,
NJ)
|
Family
ID: |
22879535 |
Appl.
No.: |
05/234,018 |
Filed: |
March 13, 1972 |
Current U.S.
Class: |
356/5.12;
250/221 |
Current CPC
Class: |
G01S
17/36 (20130101); G01S 7/491 (20130101) |
Current International
Class: |
G01S
17/00 (20060101); G01S 7/48 (20060101); G01S
7/491 (20060101); G01S 17/32 (20060101); G01c
003/08 (); G06m 007/00 () |
Field of
Search: |
;250/221 ;356/4,5
;343/12R |
References Cited
[Referenced By]
U.S. Patent Documents
Other References
Nakazawa, Japan Electronic Engineering, 7-1971, No. 56, pp.
30-36..
|
Primary Examiner: Wilbur; Maynard R.
Assistant Examiner: Buczinski; S. C.
Attorney, Agent or Firm: Lerner, David, Littenburg &
Samuel
Claims
We claim:
1. An electro-optical surveying instrument comprising:
a. a source of radiation;
b. radiation modulating means for modulating said source of
radiation at one or more frequencies,
c. reference frequency means for supplying a reference frequency
signal to said modulating means, to cause said source of radiation
to be modulated at said reference frequency,
d. radiation sensitive detection means for receiving return
radiation signals,
e. phase comparison means for comparing said reference frequency
signal with the return signal to obtain a measurement of the
distance said radiation traveled;
f. external optical path means including the total distance
modulated radiation travels from said radiation modulating means
through said instrument to a target and back through said
instrument to said radiation sensitive detection means;
g. internal optical path means including the distance modulated
radiation traverses from said radiation modulating means through
said instrument to said radiation sensitive detection means,
h. selective means for selectively measuring said internal or
external optical path means,
i. said phase comparison means including computing means for
computing the formula R = E - I + K;
where
R = range to be measured
E = external path
I = internal path, and
K = a constant,
said computing means being operative to produce signals
corresponding to the range measured,
j. display means operative from said computer means for displaying
the range measured, said external optical path means and said
internal optical path means including a common optical element said
instrument having a plumb point from which the range is computed,
and said common optical element being positioned relative to said
plumb point so as to maintain said constant K equal to zero.
2. The electro-optical surveying instrument of claim 1 wherein said
common optical element include a first beam splitter, said first
beam splitter being positioned adjacent said radiation modulating
means to transmit radiation to said internal and external path
means, the position of said beam splitter relative to said plumb
point being operative to control the value of said constant K.
3. An electro-optical surveying instrument comprising:
a. a source of radiation;
b. radiation modulating means for modulating said source of
radiation at one or more frequencies;
c. reference frequency means for supplying a reference frequency
signal to said modulating means to cause said source of radiation
to be modulated at said reference frequency;
d. radiation sensitive detection means for receiving return
radiation signals;
e. phase comparison means for comparing said reference frequency
signal with the return signal to obtain a measurement of the
distance said radiation traveled;
f. return radiation signal comparator means for comparing, with
respect to digital levels, on a sampled basis, individual return
radiation signals,
g. said phase comparison means including computing means for
computing the distance said radiation has traveled;
h. said signal comparator being operative to prevent operation of
said computing means unless said individual sampled return
radiation signals are within predetermined digital levels, said
signal comparator means including sampling means for sampling only
one of any group, in time, of individual return radiation signals,
and display means operative from said computing means for
displaying the range measured, said sample signal being operative
to control said display means.
4. An electro-optical surveying instrument comprising:
a. a source of radiation;
b. radiation modulating means for modulating said source of
radiation at one or more frequencies;
c. reference frequency means for supplying a reference frequency
signal to said modulating means to cause said source of radiation
to be modulated at said reference frequency;
d. radiation sensitive detection means for receiving return
radiation signals;
e. phase comparison means for comparing said reference frequency
signal with the return signal to obtain a measurement of the
distance said radiation traveled;
f. return radiation comparator means for comparing, with respect to
digital levels, on a sampled basis, individual return radiation
signals,
g. said phase comparison means including computing means for
computing the distance said radiation has traveled,
h. said signal comparator being operative to prevent operation of
said computing means unless said individual sampled return
radiation signals are within predetermined digital levels, said
signal comparator means including plurality of digital level
comparators each responsive to a different digital level of return
radiation signal, a plurality of digital display means,
respectively responsive to each of said digital level comparators
to digitally display the level of a return radiation signal.
5. The electro-optical surveying instrument of claim 4 wherein said
digital display means are lamps, only one of said lamps being
energized at any time in accordance with the highest digital level
comparator energized by said individual return radiation
signal.
6. The electro-optical surveying instrument of claim 5 wherein said
lamps are neon bulbs.
7. The electro-optical surveying instrument of claim 4 wherein said
signal comparator means samples only one individual return
radiation signal out of a group, in time, of individual return
radiation signals, said individual digital display means each being
energized for a period of time equal to said sample time, in
accordance with the digital level of the sampled individual return
radiation signal as applied to said digital signal comparators.
8. The electro-optical surveying instrument of claim 7 including an
additional digital display means operative when the return
radiation signal is below the lowest level capable of energizing
one of said digital comparator means.
9. An electro-optical surveying instrument comprising:
a. A source of radiation;
b. Radiation modulating means for modulating said source of
radiation at one or more frequencies;
c. Reference frequency means for supplying a reference frequency
signal to said modulating means to cause said source of radiation
to be modulated at said reference frequency;
d. Radiation sensitive detection means for receiving return
radiation signals;
e. Phase comparison means for comparing said reference frequency
with the return signal to obtain a measurement of the distance said
radiation has traveled;
f. said reference frequency means applying, sequencially, different
reference frequencies f.sub.1, f.sub.2, and f.sub.3 of different
orders of magnitude;
g. said phase comparison means obtaining a phase measurement .phi.
with reference frequency f.sub.1, phase measurement .phi..sub.2
with reference frequency f.sub.2 and phase measurement .phi..sub.3
with reference frequence f.sub.3 ;
h. said phase comparison means including computer means for
calculating the Range R.sub.A in feet as follows: ##SPC4##
where,
R.sub.1a = .phi.1/100
r.sub.2a = r.sup.1 [(.phi..sub.1 - .phi..sub.2) -- (units digit,
R.sub.1A)]
R.sub.3a = r.sup.2 [(.phi..sub.1 - .phi..sub.3)-- (tens digit,
R.sub.2A)]
then
Range.sub.A = 1000R.sub.3A + 10R.sub.2A + R.sub.1A feet.
10. An electro-optical surveying instrument comprising:
a. A source of radiation;
b. radiation modulating means for modulating said source of
radiation at one or more frequencies;
c. Reference frequency means for supplying a reference frequency
signal to said modulating means to cause said source of radiation
to be modulated at said reference frequency;
d. Radiation sensitive detection means for receiving return
radiation signals;
e. Phase comparison means for comparing said reference frequency
signal with the return signal to obtain a measurement of the
distance said radiation has traveled;
f. Said reference frequency means applying, sequentially, different
reference frequencies f.sub.1, f.sub.2, and f.sub.3 of different
orders of magnitude;
g. Said phase comparison means obtaining a phase measurement
.phi..sub.1, with reference frequency f.sub.1, phase measurement
.phi..sub.2 with reference frequency f.sub.2 and phase measurement
.phi..sub.3 with reference frequency f.sub.3 ;
h. Said phase comparison means including computer means for
calculating the Range R.sub.M in meters as follows: ##SPC5##
where,
R.sub.1m = .phi.1/1000
r.sub.2m = r.sup.3 [(.phi..sub.1 - .phi..sub.2) -- (units digit,
R.sub.1M)]
R.sub.3m = r.sup.4 [(.phi..sub.1 - .phi..sub.3) -- (tens digit,
R.sub.2M)]
then
Range.sub.M = 1000R.sub.3M + 10R.sub.1M + R.sub.1M meters.
11. An electro-optical surveying instrument comprising:
a. a source of ranging radiation;
b. radiation modulating means for modulating said source of ranging
radiation at one or more frequencies;
c. reference frequency means for supplying a reference frequency
signal to said modulating means to cause said source of ranging
radiation to be modulated at said reference frequency;
d. radiation sensitive detection means for receiving return ranging
radiation signals;
e. phase comparison means for comparing said reference frequency
signal with the return signal to obtain a measurement of the
distance said radiation has traveled;
f. electrical power supply means for supplying electrical energy to
operate the instrument; and
g. initiate means operative to initiate operation of said
instrument, said initiate means including a source of light
modulated at a high frequency mounted on said instrument, a light
sensing means adjacent said light source but out of the path of
radiation of said light source and positioned to receive reflected
radiation from said light source by means of a reflective surface
positioned adjacent said light source but spaced therefrom,
electrical filter means connected to the output of said light
sensing means to pass only high frequency signals from said light
sensing means to initiate operation of said instrument.
12. The electro-optical surveying instrument of claim 11 wherein
said high frequency source of light is energized by said reference
frequency means.
13. The electro-optical surveying instrument of claim 11 wherein
said high frequency source of light is a photo emitting diode.
14. The electro-optical surveying instrument of claim 13 wherein
said light sensing means is a photo-sensitive semiconductor
device.
15. The electro-optical surveying instrument of claim 14 wherein
said electrical filter means is a capacitor connected to the output
of said photosensitive semiconductor device.
16. A finger operated switch comprising a high frequency radiation
source, radiation sensing means, mounting means for mounting said
radiation source adjacent said radiation sensing means but out of
the path of said radiation source and said sensing means positioned
to relfected radiation from said radiation source when a reflective
surface is positioned adjacent said radiation source but spaced
therefrom; and
high frequency electrical filter means connected to the output of
said radiation sensing means to pass only high frequency signals
from said radiation sensing means to thus provide a signal
indicative of the positioning of a reflective surface adjacent said
radiation source; said last mentioned signal operative to initiate
operation of equipment associated with said switch.
17. The switch of claim 16 wherein said radiation source is a
photoemitting diode.
18. The switch of claim 17 wherein said radiation sensing means is
a photosensitive semiconductor device.
19. The switch of claim 18 wherein said high frequency filter means
is a capacitor connected to said radiation sensing means.
Description
BACKGROUND OF THE INVENTION
Electro-optical equipment for distance measurement has been known
for many years. With the advent of different sources of light
intensity, new retroreflectors, advances in electronic and computer
technology, it has been possible to increase, significantly, the
range and accuracy of these instruments so that they become a
necessary tool for the surveyor. In the past, a laser distance
measuring device was operative to transmit a coaxial beam at a
retroreflector positioned at a target. This beam was then returned
to the instruments coaxially and focused onto a receiving
photodiode. Through various methods including an iris or variable
aperture, the intensity of the returned light is controlled. The
laser is modulated by a multitude of frequencies with the distance
accuracy being determined by the number of frequencies utilized to
modulate the laser. The light impinging upon the photodiode from
the distance reflector is then compared to the light impinging on
the photodiode from the internal path of light of the laser and
substracted one from the other to obtain the range measured (the
range equal to twice the actual distance to the target). Then, an
internal correction must be made for inaccuracies in the
instrument, which are constant, as the actual distance measured is
not the distance from the plumb point of the instrument to the
target. After the instrument has been built, measurements are taken
to determine the instrument correction factor and provision is made
for dialing in the instrument correction factor so that the reading
of the instrument will be accurate. To this time, there has been no
means for designing the instrument so that such instrument
correction is not required.
In order for the system to operate properly, the return signal must
be of sufficient intensity so as to give a clear reading, well
within the sensitivity of the instrument, and one which can be
easily read without error. Further, the signal should not be too
high, as this type of signal with its sharp wave fronts also create
problems. In the past other instruments have utilized meters to
indicate to the user of the instrument that the incoming signal was
in the correct range for a reading. However, any meter, of the
so-called analog type, has a built in averaging factor and does not
indicate when only one or two of every fifty pulse signals is of
sufficient strength to be read. In such a situation an averaging
type meter will indicate that there are no signals which can be
read and the surveyor would normally give up hope of measuring.
However, if a meter could be provided which would indicate to the
user that at least some signals are coming in which are useable,
the surveyor can wait until sufficient signals have been received
by the instrument over a greater period of time so as to get a
complete and accurate reading.
For reasons that have never been wholly explained, when one
averages a frequency modulated laser beam over a number of readings
to come up with a desired distance measurement, there appear to be
a wide range of errors created by a form of second harmonic
distortion, which second harmonic distortion can, in fact, create
significant misreadings. To avoid this, in the past, this type of
error has been corrected by inserting a coil or other 90.degree.
phase shifting element into the system after half of the readings
were completed, prior to averaging, then shifting the outgoing
signal by 90.degree. through a coil for the next set of readings so
that, during averaging, all of second harmonic distortions would be
canceled out, assuming the second harmonic distortion remained the
same during the next group of readings.
In the past, where measurements were being made of long distances,
it was well known that one had to have more than one frequency when
the distance to be measured was longer than one half the wave
length of the modulating frequency. Utilizing this system, the
first wave length was normally set so as to read the first unit of
measurement, for example, up to X.XXX meters. Combining two
frequencies, it is possible to get a phase measurement which would
give the information for XO.OO measurement which in combination
with the first measurement would give up to 99.999 meters in range.
With a third frequency, the range could be expanded to OXOO.OOO
meters in range thus giving a total range of XXXX.XXX meters range.
It was thought that, utilizing this system, four frequencies were
required to achieve the accuracy necessary to measure XXXX.XXX in
range.
The surveying instrument of the type above described is quite
delicate in that one is measuring very, very exact distances over
long ranges and it is extremely necessary to maintain no movement
of the instrument during measurement which could cause error. Up
until now, one of the major problems of the instrument was turning
it on and off. To push a button for the instrument to start up
might well move the instrument even very slightly so as to cause an
error. To avoid this problem, various types of capacitive switches
were developed which required only that the surveyor touch the
instrument to turn it on or off. However, there has been no
touchless switch for a surveying instrument which would effectively
avoid all of the problems relating to turning the instrument on and
off which have been found in the past.
SUMMARY OF THE INVENTION
The internal calibration of the instrument can be effected by
placing the optics and selecting the path length in such a manner
that the equation R = E minus I is exactly satisfied by the
instrument wherein:
R is the range measured
I is the internal optical path length from the laser to the
photodiode and
E is the external optical path length from the laser, to the object
being measured back to the photodiode.
The system can be set up so that the instrument offset is simply
and accurately determined as a measure of the placement between the
plumb point of the instrument and the zero offset plane. Thus, one
need merely move the plumb point of the instrument in its
manufacture to obtain zero offset. Alternatively, if there is a
value for the offset other than zero, by understanding the
equations by which such offset is calibrated even before the
instrument is put together, it is only necessary to place such
information into the logic computor memory which would then
automatically compensate for the instrument error with each
measurement.
The present system further includes a digital signal level
indicator which gives a digital visible indication of the level of
incoming pulses to indicate whether any pulses are available which
can be read by the instrument. In this regard, for every thirty two
pulses that are received, one pulse is sampled as to its level, and
that level is indicated on a digital display and held for 32
additional pulses until another measurement can be made. This gives
sufficient time for the viewer to observe the value of these
sampled pulses without the necessity of averaging the level of all
of the pulses during any given period. By utilizing selected pulses
and then holding their result for the 32 pulse count, it is
possible to obtain an indication of the value of at least one pulse
in every thirty two. Further, a system which measures these pulses,
is further operative to thus space the sampling of pulses so that
the pulses are not taken too close together which might cause an
inaccurate reading to be received wherein there is a short time
period fluctuation of the signal received. By sampling at spaced
intervals the short irregularties can be averaged out over a longer
period of time.
The digital signal level indicator further provides means for
signaling the computer to select only signals of a given level and,
when dealing with the less significant figures, in measurement, can
provide a greater window of pulses which can be utilized for
measurement.
In contradistinction to the prior art utilization of shifting,
90.degree., the phase of the modulated signals applied to the
laser, the present invention contemplates electronic phase shifting
in the logic circuit associated with the reference oscillator so
that there is truly effective, exact, 90.degree. phase shift of the
signal. It will easily be understood that, when coils were used to
obtain the 90.degree. phase shift, a given coil could provide a
different impedance for different frequency signals and, thus, it
may not be possible to have an exact 90.degree. phase shift for
each of the signals which were included in the modulating signal
applied to the laser. Since there are a plurality of frequencies
applied thereto, it is possible to have minute variations in delay
which can cause errors. By electronically phase shifting the
signals as in the present invention, this type of error is
avoided.
The "off-on" switch for the surveying instrument of the present
invention is operative by utilizing a photoemitting diode energized
from the high frequency source of the instrument itself so as to
emit light at that high frequency level. Adjacent the photoemitting
diode is a photosensitive semiconductor which, of course, will pick
up lights and produce an electrical signal in accordance therewith.
Ordinarily, the photoemitting diode's light is not directed at the
phototransistor and, therefore, does not effect the phototransistor
at all. The only light which hits the phototransistors is ambient
light and this is at a very low frequency (sun light is almost a
steady state). The output of the photosensitive semiconductor is
connected through a high pass filter to an amplifier. When light
from the photo emitting diode is reflected back onto the
photosensitive diode, an electrical signal proportional in
frequency to the frequency of the energization of the photoemitting
diode is transmitted, through the high pass filter, to the
amplifier of the instrument, thus giving a start pulse. It is thus
only necessary to reflect the output light of the photo emitting
diode back on to the photosensitive device surface to turn "on," or
provide a start signal to the instrument. If one's finger is placed
relatively close to the photoemitting diode it will, effectively,
provide such reflective surface so as to achieve this result. It is
thus possible to initiate a start signal without touching the
instrument as it is only necessary to go near enough to the photo
emitting diode so as to cause reflection of light emitted therefrom
back onto the photosensitive device in the instrument.
In the present system, three frequencies are used to modulate the
laser beam with the first return phase data being operative to
develop a signal up to 10 meters, the second return phase data from
the second frequency, being operative to combine with the first
phrase signal to provide significant numbers which can be utilized
between 10 and 1000 meters; and the third phase data received at
the third frequency, when combined with the first and second
frequency signals, being operative to provide the significant
figure 10.sup.4 meters. It would further be obvious, that the
system can be operated to provide an output either in meters or in
feet depending upon the system utilized. Thus, it will be seen that
the metric instrument reading will require three calculations and
will be composed as follows: ##SPC1##
where
R.sub.1m = .phi.1/1000
R.sub.2m = R.sup.3 [(.phi..sub.1 -.phi..sub.2)--(units digit,
R.sub.1m)]
R.sub.3m = R.sup.4 [(.phi..sub.1 -.phi..sub.3)--(tens digit,
R.sub.2m )]
Then
Range.sub.m = 1000 R.sub.3m + 10 R.sub.2m + R.sub.1m meters
This is then rounded off to the nearest tens of meters, and is then
rounded off to the nearest thousands of meters.
DETAILED DESCRIPTION OF THE DRAWINGS
FIG. 1 is a block schematic diagram of distance measuring
instrument of the present invention.
FIG. 2 is a block diagram of the modulator and scintillation
detector and display shown in FIG. 1.
FIG. 3 is a diagrammatic showing of the lens system of the present
invention.
FIG. 4 is a schematic diagram of the switch utilized on the
distance measuring apparatus of the present invention.
In FIG. 1, the distance measuring instrument of the present
invention is generally designated by the numeral 10. The instrument
10 includes a helium-neon laser 12 (Hughes Model 3180) which is
modulated at three frequencies by an electro-optical light
modulator 14 (Isomet KD*P) which includes a potassium deuterium
phosphate crystal. The electrical optical light modulator 14 is
controlled by a signal received from a power amplifier 16, which
amplifier amplifies one of the output signals from an oscillator
18.
The oscillator 18 transmits to the power amplifier 16 a signal at
an upper side band frequency (F.sub.1) equal to the sum of the
reference frequency (F.sub.1 ') of a crystal oscillator in the
oscillator 18 and an intermediate frequency that is derived from
and is 10.sup.4 less than the reference frequency. The phase
measurement is made at the intermediate frequency obtained by down
converting the received frequency with the reference frequency.
Within the oscillator module 18, the reference frequency is divided
by 10.sup.2 and 10.sup.3 to obtain signals of approximately 150KHz
and 15KHz. These two signals are combined with the basic reference
signals (F.sub.1 ') to obtain two other reference signals (F.sub.2
') and (F.sub.3 ') respectively. The two new references signals are
then combined with the intermediate frequency to obtain two other
transmission signals F.sub.2 and F.sub.3. By appropriate analog
gating techniques, the transmission and reference signals are
activized in pairs F.sub.1 and F.sub.1 ', F.sub.2 and F.sub.2 ',
and F.sub.3 and F.sub.3 ' by corresponding logic gates from the
logic computer to the gate inputs G.sub.1, G.sub.2 and G.sub.3
respectively. Thus, all required frequencies are obtained from a
single oscillator crystal. A terminal G.sub.4 is provided for the
oscillator 18 so that, in a manner which will be discussed below,
after 50 pulses have been counted, the oscillator 18 will be
shifted in phase 90.degree. for the next 50 counts. Counting in
this way, eliminates all distortions due to the second harmonics,
which distortions have been previously been effected by placing
90.degree. phase shifters between the power amplifier 16 and the
electro-optical light modulator 14. By doing the phase shifting
electronically, rather than by inserting a loss member, more
arcuate readings are possible without distortion to the transmitted
signal.
It should be noted, for reasons which will be discussed below, that
only three reference frequencies are required when spanning a
range, which is capable of providing the same distance measurement
as distance measuring instruments utilizing four reference
frequencies.
The output from the electro-optical light modulator is transmitted
through an optical system best shown in FIG. 3 and controlled by an
internal solenoid 20 and directed at a target retroreflector. The
beam is transmitted coaxial to the retroreflector so that the
return light beam is received back through an iris diaphragm 22
onto a receiving diode and amplifier 24. The iris diaphragm 22 is
variable so that it may be properly set at a desired return signal
level. The receiving diode and amplifier 24 includes a photo diode
(Texas Instruments Integral diode and Amplifier TIXL-79). The
output of the receiving diode and amplifier 24 is fed to a
demodulator and scintiliation circuit 26. This return radio
frequency signal is demodulated with respect to the reference RF
signal from oscillator 18 which also supplies the reference IF to
the demodulator and scintillation detector 26. The gain of the
intermediate frequency signal is set by a gain control knob 28 on
the panel 30 of the instrument. Also on the panel 30 is a suitable
display 32 which consists of a series of seven bulbs 134 which
indicate the signal level being received by the receiving diode and
amplifier 24. The display is set up so that one attempts to make
sure that only the center bulb of the seven bulbs 134 is in fact
operative indicating that a correct signal is being received for
measurement. The operation of this circuit will better be discussed
with respect to FIG. 2. Also in the display 32 there is shown the
seven figures of the final measurement being made.
It should be noted that for each signal being read, the instrument
is calibrated for the internal path of the instrument itself so
that the final distance measured is in fact the distance from the
plumb center of the distance measuring instrument to the
refroreflector at the target. The demodulator and scintillation
detector 26 feeds a start pulse to a logic computer 34 which does
the measurement for the distance and provides the final distance
measurement to the display 32. The logic computer 34 is supplied
with the reference IF signal and the clock signal from the
oscillator 18. The start up of the instrument is controlled by a
suitable start button 36 on the instrument panel itself, which is
more fully described in FIG. 4. The panel 30 further has thereon a
switch 38 which merely sets the logic 34 so that a readout will be
in either feet or meters depending upon the needs of the user.
Atmospheric correction is supplied to the logic circuit by a
control 40 on the instrument panel and, thus, at the end of any
given reading, a suitable correction will be made for the
particular atmospheric conditions so that one will provide a direct
reading on the display 32 of the actual distance measured.
The entire instrument 10 is supplied suitable power from a power
source 42 and the solenoid 20 is operated by suitable "Off" "On"
and internal external control 44. There is no need for calibrating
internal offset in the instrument for reasons that will be
discussed with respect to the arrangement in FIG. 3.
Since the phase measurement is made at an intermediate frequency,
the return signal at the intermediate frequency is obtained by
mixing at the demodulator 26 the return RF with a reference signal
that differs from the transmitted signal by 1.498 KHz. Three
frequencies are involved, as was discussed previously. They will
produce three readings, .phi..sub.1 ; .phi..sub.2 ; and
.phi..sub.3. .phi..sub.1 will provide a reading from 0.1 ft. to 10
ft. or 1 mm to 10 mm; .phi..sub.2 will provide a reading from 10
ft. to 1000 ft. or 10 m to 1 km; and .phi. .sub.3 will provide
readings from 1000 ft. to 10,000 ft. or 1 km to 10 km.
The phase measurement is made between the start pulse zero cross
detection 50 of FIG. 2 to the logic circuit 34 and a stop pulse at
the reference I.F. which is received from the oscillator 18. Since
the clock pulses are measured between the start pulse and the stop
pulse, the total count is a fractional part of the half wave length
of the modulated frequency. For the basic frequency, F.sub.1 equal
14.989625 MHz with a half wave length of ten meters, the least
count is one millimeter. The other frequencies of F.sub.2 equal to
14.974635 MHz and F.sub.3 equal to 14.839279 MHz are used to
determine the range.
Using the general functional requirements, the first step is to
acquire phase data:
1. F.sub.1, .PSI..sub.1, return 2. F.sub.1, .PSI..sub.2, return 0 -
10 meters .phi..sub.1 * 3. F.sub.1, .PSI..sub.1, calibrate 0 -100
feet 4. F.sub.1, .PSI..sub.2, calibrate 5. F.sub.2, .PSI..sub.1,
calibrate 6. F.sub.2, .PSI..sub.2 , calibrate 10 - 1000 meters
.phi..sub.2 * 7. F.sub.2, .PSI..sub.1, return 100 - 10.sup.4 feet
8. F.sub.2, .PSI..sub.2, return 9. F.sub.3, .PSI..sub.1, return 10.
F.sub.3, .PSI..sub.2, return 1000 - 10.sup.4 meters .phi..sub.3 *
11. F.sub.3, .PSI..sub.1, calibrate 10.sup.4 - 10.sup.5 feet 12.
F.sub.3, .PSI..sub.2 , calibrate *.phi..sub.1, .phi..sub.2,
.phi..sub.3 are summations of .PSI..sub.1, .PSI..sub.2, acquired in
return and calibrate positions on respective frequencies.
The American system instrument reading will require three
calculations and will be composed as follows: ##SPC2##
where,
R.sub.1a = .phi..sub.1 /100
r.sub.2a = r.sup.1 [(.phi..sub.1 - .phi..sub.2) -- (units digit,
R.sub.1A)]
R.sub.3a = r.sup.2 [(.phi..sub.1 - .phi..sub.3) -- (tens digit,
R.sub.2A)]
then
Range.sub.A = 1000R.sub.3A + 10R.sub.2A + R.sub.1A feet
R.sup.1 indicates that R.sub.2A is rounded off to nearest tens of
feet. R.sup.2 indicates that R.sub.3A is rounded off to nearest
thousands of feet.
The metric system instrument reading will require three
calculations and will be composed as follows: ##SPC3##
where,
R.sub.1m = .phi..sub.1 /1000
r.sub.2m = r.sup.3 [(.phi..sub.1 - .phi..sub.2) -- (units digit,
R.sub.1M)]
R.sub.3m = r.sup.4 [(.phi..sub.1 - .phi..sub.3) -- (tens digit,
R.sub.2M)]
then
Range.sub.M = 1000R.sub.3M + 10R.sub.2M + R.sub.1M meters
R.sup.3 indicates that R.sub.2M is rounded off to nearest tens of
meters. R.sup.4 indicates that R.sub.3M is rounded off to nearest
thousands of meters.
For example, if .phi..sub.1 was measured at 1348.642; .phi..sub.2
at 1335.156; and .phi..sub.3 as 1347.293 and R.sub.1A equals to
8.642; R.sub.2A equals 1348.642 - 1335.156 - .086 or 0340.000; and
R.sub.3A equals 1348642 - 1347.293 - .349 or 1000.00. Thus the
distance measured would be 1348.642 meters.
In FIG. 2, there is a more detailed description of the operation of
the demodulator and scintillation detector 26 display 32, and gain
set 28.
As was described previously, the demodulator and scintillation
detector 26 receives a return signal that is the upper side band of
the reference signal and the intermediate frequency in a phase
displaced relationship in accordance with the distance traveled.
This signal RF is fed to a separate demodulator 46 and mixed with
the reference RF to produce a resultant IF signal which is more
easily measured. The output of demodulator 46 is fed through a gain
set potentiometer 28 to a tuned amplifier 48 which is tuned to
amplify the IF signal which is approximately 1.5 KHz. A zero cross
detector 50 produces a start pulse which starts a pulse signal when
the output of tuned amplifier 48 crosses zero going negatively,
which start pulse is the start pulse shown in FIG. 1 fed through
the logic computer 34.
The output of tuned amplifier 48 is also supplied along a common
input line to a group of six comparator circuits 54, 56, 58, 60, 62
and 64. The comparator circuits 54 56, 58, 60, 62 and 64 have one
input connected through a suitable capacitor and resistor to line
52 and the other input thereof connected from a source of DC
potential on line 66 through respective calibrator resistors 68,
70, 72, 74, 76 and 78. The calibrating resistors 68, 70, 72, 74, 76
and 78 are set so that they will provide different voltage levels
from the lowest voltage level being at the input of the amplifier
64, to a higher voltage level in comparator 62 and a still higher
level at comparator 60; and so on to the highest level in
comparator 54. Unless the input on line 52 exceeds the reference
potential on a particular comparator, there will be no output for
the comparator. Thus, low level signals might only produce outputs
at the comparators 64 and 62 and not any comparator thereabove. It
is to be noted that the outputs of the comparators 56, 58, 60 and
62 have been respectively designated as W, X, Y and Z. Thus, it is
intended with a good return signal, that the amplifier signal
should be sufficiently high so as to energize either comparator 58
and/or 60, but it is sufficient for the secondary measurement that,
at least, the comparators 56 or 62 can be used. Thus, on the first
frequency signal used, it is desired to measure only signals which
pass through comparator 60 as a greatest lower boundary but do not
pass through comparator 48 as a least upper boundary. For this
reason, these XY pulses are supplied to the logic computer as part
of the narrow window pulse shown in FIG. 1. After the frequency F1
has been measured, and the secondary frequencies are used, there is
a switch-over to the wide window signal of W through Z and that
signal is also supplied to the logic computer 34. It will be
understood that it is possible to vary the signals levels by one or
two means. First, by varying the gain set potentiometer 28 as shown
in FIG. 2 or by varying the iris opening 22 in FIG. 1 so as to
control the amount of the return signal.
It will be understood that the window pulses are operative to
control whether the logic computer will read a particular signal or
will not read that particular signal. That is, if the X-Y narrow
window is enabled, it allows the logic computer to read the pulses
being fed thereto. If it is not enabled, no pulse will be read.
This is to avoid ambiguous signals such as would occur with very
low level signals or, very high level signals caused by spurious
reflections and the like.
It is very desirable for the operator of the instrument to know
whether the return signal fits within the window to be measured so
that he can adjust the gain set 28 or iris 22 to achieve exact
readings. In the past, an analog meter was used to determine
whether the return signal level was within a desired range to be
measured. However, when only one or two signals were being received
which were within range, the analog meter was unable to detect such
signals as it integrated return signals over a period of time and,
accordingly, the operator believed that he could not take a reading
when in fact there were some signals which were capable of being
read. The only problem was that it would take a long time to
receive sufficient signals to give a proper reading. However, in
distance surveying, it is not unreasonable for an instrument to be
set for a reading and to wait a minute or two for the purposes of
determining or obtaining sufficient return signals at proper levels
to give an accurate reading. This, effectively, enhances the range
of the instrument if the operator knows that he can get some
signals of value for a reading. For this reason, every thirty
seconds a pulse of the up frequency (every 22 milliseconds) is fed
forward in a manner which will be discussed below to determine at
what level the signal has been received. For this purpose, the
reference IF at 1.5 KHz is applied to a divider circuit 84 through
a gate 86 to produce a pulse on line 88 for every 32 pulses
received at the input divider 80. Similarly, through the use of two
divider circuits 90 and 92, a pulse is received on line 94 also
every 32 pulses but these pulses occur immediately before the
pulses on line 88. The pulses on line 94 thus clear the flip flops
to await the next impulse for resetting. Line 88 is connected to a
series of gates 96, 98, 100, 102, 104 and 106 which have connected
to their other inputs the outputs, respectively, of the comparators
54, 56, 58, 60, 62 and 64. Thus, if there is a signal on both the
inputs at one of the gates 96, 98, 100, 102, 104 and 106, then
there is a signal at their output. The output of each one of these
gates 96, 98, 100, 102, 104 and 106 is applied to a flip flop
circuit 108, 110,112, 114, 116 and 118 respectively. It should be
noted that the flip flop circuits 108, 110, 112, 114, 116 and 118
are connected up to seven gates 120, 122, 124, 126, 128, 130 and
132 whose outputs control seven lamps 134, with the lowermost lamp
designated as 136 and the remaining lamps being in order of the
magnitude 138, 140, 142, 144, 146 and 148. Lamps 134 are part of
the display 32 shown in FIG. 1. It will be noted that even if the
lowermost flip flop 118 is not energized, one of its outputs,
connected to the gate 132 will have a voltage thereon energizing
lamps 136. This will indicate that there is not even a minimum
signal level along the input line 52. If there is an input on line
42 sufficient to cause the comparator 64 to have an output signal,
and that signal is present on the thirty second pulse as it is
transmitted on Line 88, then gate 106 will transmit a pulse to flip
flop 118, causing it to reverse, shutting off the gate 132, and
therefore turning off light 136 and providing a signal to the
lowermost terminal of gate 130. The gate 130 only passes signals
when both of its inputs have a signal thereon. Since gate 116 does
not have an input thereto, its uppermost terminal does have a
signal thereon causing neon line 138 to be turned on. This would be
the only lamp that would be turned on. Similarly, working up the
line, when comparator 62 is energized, the gates 104 and 106 have a
signal thereon, preventing gate 130 from operating but allowing
gate 128 to pass a signal to light the lamp 140. It can thus be
seen that lamp 142 is comparable to having a signal at terminal Y
and it will be normal for the operator to set gain set 28 and the
iris 22 at a level so that the neon lamp 142 is always being lit.
It should further be noted that the logic computer is operative so
that when the beam first is at F.sub.1 is transmitted by the laser
12, its only return beam is measured when the signals fit within
the X-Y narrow window. However, when there is a switchover to
frequencies F.sub.2 and F.sub.3, the logic computer will accept
signals fitting within the wider window W-Z.
The signal on line 94 is operative to reset all of the flip flops
108, 110, 112, 114, 116 and 118 back to their original positions.
In between, pulses are being received so that each succeeding pulse
can be read. It should be further noted that in effect a signal is
being sampled every thirty two pulses to determine whether the
return signal is sufficient for the range to be measured and that
signal is being applied through bulbs 134 which have a time build
up and decay period far longer than the length of any single pulse.
Thus the sampled pulse serve the purpose of providing a longer
signal to operate the fast response (22 millisecond rise time)
filament bulbs and the bulbs provide the service of supplying a
visual signal over a longer period of time indicating the level at
which an individually sampled signals is being received by the
instrument.
In FIG. 3, there is shown the optical system for the distance
measuring device of the present invention. That is, as was
previously discussed, the laser 12 transmits a beam through
reflected mirror 150 and 152 to electro-optical light modulator 14.
The light modulator 14 then transmits its signal through analyzer
154 to a beam splitter 156. The beam splitter 156 sends the output
of the laser directly through a lens t6 into a 45.degree. mirror
158. The distance between the center of the beam splitter 156 and
the mirror 158 is a.sub.2. The distance between the output of the
electro-optical light modulator 14 and beam splitter 156 is
a.sub.1. Light transmitted through beam splitter 156 to mirror 158
is then reflected off a second mirror 160 toward the target which
is in the form of a retroreflector 162. The distance between mirror
158 and mirror 160 is a .sub.3. Light bouncing off mirror 160
passes through a lense t.sub.8 toward the retroreflector 162. The
distance between the outer surface of lense t.sub.8 and
retroreflector 162 is L. The distance between mirror 160 and the
back surface of lense t.sub.8 is a.sub.4. The returned light of the
retroreflector 162 passes back through the lense t.sub.8 and is
focused on the receiving diode 24.
The beam splitter 156 further transmits the output of
electro-optical light modulator 14 toward another mirror 164.
Internal solenoid 20 is operative to cut off light returning from
retroreflector 162 and prevent a beam from returning to the
receiving diode 24 while opening the path between beam splitter 156
and mirror 164. Alternatively, the internal solenoids cuts off the
internal light path between beam splitter 156 and mirror 164 and
opens the path from the retroreflector 162 to the diode 24. Thus
the internal solenoid is utilized to select which path is to be
measured, namely, the external path to the target or the internal
path all as will be described hereinafter.
The internal path continues from the mirror 164 back to the
receiving diode 24. The mirror 164 is positioned so that the
distance between beam splitter 156 and mirror 164 is exactly equal
to the distance between the mirror 158 and mirror 160 or a.sub.3.
Further, the distance between the beam splitter 156 and mirror 158
is exactly equal to the distance between mirrors 164 and 160 or
a.sub. 2. The plumb axis of the instrument is designated as 166.
This axis can be preset when manufacturing the instrument. The
distance between the plumb axis 166 and the mirror 164 as
designated a.sub.5, whereas the distance from plumb axis 166 to
receiving diode 24 is designated as a.sub.6.
Most instruments presently made provide a "zero offset" computation
or correction switch so that the individual operator must calibrate
the instrument for "zero offset." It would be desirable to avoid
the necessity of this type of computation in the field and to build
an instrument with a true zero offset without any need for
precalculation in the field. To achieve this, the present invention
is operative to position lens 164 relative to plumb axis 166,
mechanically, on the instrument so that the range actually measured
is truly equal to the external light path minus the internal light
path without any correction.
To achieve this, the present invention operates as follows:
One views the distance to be measured through a suitable viewing
telescope 168 on the instrument. As was indicated, it is desired to
measure the range and set it exactly equal to the external optical
path length minus the internal optical path.
The range to be measured is given the designation R; The distance
from t.sub.8 to the point to be measured is designated L; the
internal optical path length is designated I; The external optical
path length is designated by E; and the index of refraction of the
optical material utilized is designated as "n."
With a given instrument, it can be seen that the range R
equals:
R = (2a.sub.5 + 2a.sub.2 + 2a.sub.4 + 2t.sub.8 +2L)
I = a.sub.1 + a.sub.3 + a.sub.5 + a.sub.6
E = a.sub.1 + 2a.sub.2 + a.sub.3 + 2a.sub.4 + 2t.sub.8 + 2L +
a.sub.5 + a.sub.6 + (n - 1) (t.sub.6 + 2t.sub.8)
For zero offset, the following equation must be met:
R = E - I
Therefore, 2a.sub.5 = (n - 1) (2t.sub.8 + t.sub.6),
for zero offset:
a.sub.5 = (n - 1)/2 (2t.sub.8 + t.sub.6)
Since t.sub.8, t.sub.6 are known quantities, it is merely necessary
to set the pivot point 166 at a distance which satisfies the above
equation. An alternative to the above, where it was not physically
possible to change the plumb axis of the instrument or to move
lenses 156 and 164 in accordance with the above equation, then,
when the value of the equation; R = E - I + K is determined, as
above, where "K" is the offset, this amount can be preset into the
logic computer 34 so that when all calculations are arranged zero
offset is automatically set into the equation. However, it can be
understood that by building this amount into the instrument so that
there is no zero offset required, one saves on logic computer
elements and time of operation.
As one can see, the distance between the measuring device and the
present invention is intended for extremely accurate usage. One of
the real problems in working with this type of instrument is the
simple problem of turning it on and off without anyone disturbing
the physical setting of the instrument so as to cause a change to
require recalibration for error. It thus would be very desirable to
have, as a part of the instrument, a system of turning the
instrument on or off for the purpose of initiating measurement
which would not require touching the instrument. This device is
shown in FIG. 4 and is generally designated as in FIG. 1 by the
numeral 36. That is, there is provided a transistor 170 which
received a high frequency signal from the reference IF, such that
the output of transistor 170 energizes a photo diode 172 which
emits light at a frequency of 1.5 KHz. This light emitting diode is
on the front panel of the instrument 30 and, if one were to place
ones finger or some other external surface 174 adjacent the light
emitting diode 172 it would reflect the light upon the
photosensitive transistor 176.
The photosensitive transistor 176 is capacitively coupled to a high
pass filter 178, and then to the base of a transistor amplifier
180. Thus, normally, ambient light or room light is almost at a
D.C. level and, no matter how much such light excites the
photosensitive transistor 176, the output thereof will not pass
through high pass filter 178 to the base of transistor 180 and
there will be no output for a start pulse. However, if light is
reflected off surface 174 onto light sensitive transistor 176 from
diode 172 then, one would have a pulsating output at 1.5 KHz which
would be passed by high pass filter capacitor 178 through
transistor 180 causing an initiate pulse to be sensed at the logic
computer 34 indicated at the start of operation. It should be noted
that it is not necessary for someone to touch the instrument as it
is only necessary to bring one's finger close enough to the light
emitting diode 172 so as to cause reflection thereof onto light
sensitive transistor 176 resulting in an "initiate" pulse.
The output of transistor 180 has a suitable pulse shaping capacitor
182 thereacross.
Although this invention has been described with respect to its
preferred embodiments, it should be understood that many variations
and modifications will now be obvious to those skilled in the art,
and it is preferred, therefore, that the scope of the invention be
limited not by the specific disclosure herein, only by the appended
claims.
* * * * *